Conventionally, a packaging tray is used to package a display element, such as an LC (Liquid Crystal) panel. To transport assembled individual display elements, at least one display element is placed in each packaging tray, then the packaging trays are stacked in layers and sealed in a corrugated cardboard box. When the display elements are transported while being held in the packaging trays in the above manner, the damages to the display elements during the transportation can be minimized.
Well-known examples of the conventional packaging trays used for the transportation include:
1 molded articles made of non-foam materials using a vacuum molding cast; PA1 2 molded articles made of foam materials, such as Styrofoam; and PA1 3 assemblages of corrugated plastic or polyethylene foam. PA1 at least one display element holding concave portion for holding the display element; and PA1 a position determining portion, provided near each side of the packaging tray, for, when a plurality of packaging trays are stacked, fixedly determining a stacking position of each packaging tray with respect to at least one of other packaging trays placed above and beneath.
The examples also include a packaging tray disclosed in, for example, Japanese Laid-open Patent Application No. 324674/1996 (Tokukahei No. 8-324674). The packaging tray disclosed in the above publication has a lid-wise outside shape, so that a plurality of the packaging trays can be readily stacked in layers, which will be explained more in detail in the following.
As shown in FIG. 12(a), a packaging tray 51 disclosed in the above publication is made of a conductive material prepared by blending carbon with polystyrene or vinyl chloride, which is made into a lid-wise shape using a cast.
The packaging tray 51 includes a plurality of display element holding concave portions 52. A portion indicated by a capital letter R in FIG. 12(a) is depicted in FIG. 12(b) illustrating an enlarged bottom portion of one display element holding concave portion 52. As shown in the drawing, the display element holding portion 52 includes corner stoppers 53, a side surface stopper 54, and holders 55.
The corner stoppers 53 touch three out of four corners of an LC panel 56 (see FIG. 12(c)) to set these corners at their respective right positions. On the other hand, the side surface stopper 54 touches one side surface near the remaining corner to set the LC panel 56 to a right position. Therefore, the LC panel 56 is held at a predetermined position inside the packaging tray 51 by being set in the right position with the corner stoppers 53 and side surface stopper 54.
As shown in FIG. 12(c) illustrating a sectional view taken on line 12(c)--12(c) of FIG. 12(a), the holders 55 hold the LC panel 56 by receiving the same on the back surface at a portion outside an effective display area A of the LC panel 56. Accordingly, the damages to a polarizing plate placed inside the effective display area A of the LC panel 56 can be prevented.
Also, as shown in FIG. 12(a), a rib 57 having a concave cross section is provided along the edge of each side of the packaging tray 51 on the surface thereof, whereby the warpage of the packaging tray 51 while the packaging tray 51 is molded or the LC panels 56 are held in the display element holding concave portions 52 can be prevented.
On the other hand, as shown in FIG. 13, spacers 58 are provided on the back surface of the packaging tray 51 at a portion where the display element holding concave portions 52 are not formed, that is, at the corners and almost at the center of the packaging tray 51. The spacers 58 touch the surface of another packaging tray 51 placed beneath when a plurality of the packaging trays 51 are stacked in layers vertically.
FIG. 14 illustrates a plurality of the packaging trays 51 stacked in layers vertically. In the drawing illustrating the cross section, the spacers 58 of the upper packaging tray 51 seem to have fitted into the ribs 57 of the lower packaging tray 51, but in practice, the spacers 58 of the upper packaging tray 51 only touches the surface of the lower packaging tray 51, which is apparent from the position of the spacers 58 with respect to the ribs 57 shown in FIGS. 12(a) and 13.
Since the spacers 58 are provided on the back surface of the packaging tray 51, when a plurality of the packaging trays 51 are stacked in layers vertically, an adequate space is secured between the LC panels 56 held in the lower packaging tray 51 and the upper packaging tray 51, thereby preventing physical contact between the LC panels 56 and upper packaging tray 51. Consequently, it has become possible to prevent a load from being applied on the surface of the LC panels 56 held in the packaging tray 51, and therefore, the damages to the LC panels 56 can be eliminated.
However, since the spacers 58 provided on the back surface of the upper packaging tray 51 only touch the surface of the lower packaging tray 51, the stacking position of the lower packaging tray 51 with respect to the upper packaging tray 51 is not fixed. Thus, the packaging trays 51 stacked in the above manner move apart or displaced from each other due to the vibrations caused during the transportation of the LC panels 56. This reveals that the stacking position can not be controlled by merely making the packaging trays 51 into a lid-wise shape, and therefore, it is impossible to prevent the displacement of the stacked packaging trays 51 by so doing.
Thus, according to the arrangement of the above publication, the stacked packaging trays 51 can not be maintained in a stable manner. Consequently, while the LC panels 56 are transported, the packaging trays 51 are displaced from each other, which causes the sliding, chipping, or cracking of the LC panels 56, thereby posing a problem that a non-conforming ratio rises.